1. Field of the Invention
The present invention relates generally to a method for measuring stress magnitude distributed, more particularly, it relates to a method for quantitative measurement of stress in a substance which is formed of materials such as metal or resin, without damaging the substance.
2. Description of the Background Art
Generally external stress, such as tensile, shear, cleavage and peeling stress, and internal stress frequently occur in substances formed using adhesion techniques, particularly using thermal adhesion techniques. As for measuring these stresses, several methods are well known in the art. For example, in a substance formed of metals, X-Ray irradiation to the substance has been applied for measuring stress utilizing the properties of displacement of a reflection grading which is caused by uniform strain when crystals of the tested substance are subjected the stress. On the other hand, electrical measurement has also been applied utilizing the properties of the slight change of electrical resistance of an attached strain gauge when the tested substance is subjected the strain. In a substance formed of resins, the cracking properties of solvents have been utilized for measuring stress. A solvent is infused into the stressed substance then the time necessary for the generation of cracking and the size of cracks are analyzed. On the other hand, treatments such as applying a predetermined surface stress to a substance by curving it at predetermined angle are performed. Then a solvent is dropped on the curved substance. The cracking generation caused by this predetermined stress is compared to that of sample of the substance having an unknown quantity of stress. Other methods utilizing of cracking properties of the solvent have also been applied, however, all these methods estimate the stress relatively by cracking occurrence when various solvents contact with a substance having an unknown quantity of stress.
However, the methods as mentioned above require predetermined sizes of test pieces, therefore local stress measurement or estimation of actual parts, products or materials can not be accomplished easily. Additionally, measurement becomes very complicated so the time consumed in measurement becomes excessive. On the other hand, as measurements utilizing the cracking properties of solvents are essentially measurements of the breaking point of the substance relative a particular solvent, measurement of stress without breaking the tested substance can not be accomplished. Furthermore, the stress values obtained by the cracking methods as above yield results of relative estimation having only diagrammatic accuracy in the detection of stress magnitude, giving values such as high, medium and low, therefore, accurate quantification of stress is not possible.